In January Ben Hutchings reported Debian bug 841144 to the ocfs2-devel list:
https://oss.oracle.com/pipermail/ocfs2-devel/2017-January/012701.html cPanel encountered this bug after upgrading our cluster to the 4.9 Debian stable kernel. In our environment, the bug would trigger every few hours. The core problem seems to be that the size of dw_zero_list is not tracked correctly. This causes the ocfs2_lock_allocators() call in ocfs2_dio_end_io_write() to underestimate the number of extents needed. As a result, meta_ac is null when it's needed in ocfs2_grow_tree(). The attached patch is a forward-ported version of the fix we applied to Debian's 4.9 kernel to correct the issue.
From a3107e92b07ed95752d72703ee53ae71a7607098 Mon Sep 17 00:00:00 2001
From: John Lightsey <j...@cpanel.net>
Date: Mon, 20 Nov 2017 12:05:37 -0600
Subject: [PATCH] Fix OCFS2 extent split estimation for dio allocators locking.
The dw_zero_count tracking was assuming that w_unwritten_list would
always contain one element. The actual count is now tracked whenever
the list is extended.
---
fs/ocfs2/aops.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
index 88a31e9340a0..eb0a81368dbb 100644
--- a/fs/ocfs2/aops.c
+++ b/fs/ocfs2/aops.c
@@ -784,6 +784,8 @@ struct ocfs2_write_ctxt {
struct ocfs2_cached_dealloc_ctxt w_dealloc;
struct list_head w_unwritten_list;
+
+ unsigned int w_unwritten_count;
};
void ocfs2_unlock_and_free_pages(struct page **pages, int num_pages)
@@ -873,6 +875,7 @@ static int ocfs2_alloc_write_ctxt(struct ocfs2_write_ctxt **wcp,
ocfs2_init_dealloc_ctxt(&wc->w_dealloc);
INIT_LIST_HEAD(&wc->w_unwritten_list);
+ wc->w_unwritten_count = 0;
*wcp = wc;
@@ -1373,6 +1376,7 @@ static int ocfs2_unwritten_check(struct inode *inode,
desc->c_clear_unwritten = 0;
list_add_tail(&new->ue_ip_node, &oi->ip_unwritten_list);
list_add_tail(&new->ue_node, &wc->w_unwritten_list);
+ wc->w_unwritten_count++;
new = NULL;
unlock:
spin_unlock(&oi->ip_lock);
@@ -2246,7 +2250,7 @@ static int ocfs2_dio_get_block(struct inode *inode, sector_t iblock,
ue->ue_phys = desc->c_phys;
list_splice_tail_init(&wc->w_unwritten_list, &dwc->dw_zero_list);
- dwc->dw_zero_count++;
+ dwc->dw_zero_count += wc->w_unwritten_count;
}
ret = ocfs2_write_end_nolock(inode->i_mapping, pos, len, len, wc);
--
2.11.0
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